This invention relates generally to archery and more particularly relates to an adjustment apparatus that is attached to a compound bow and varies the draw weight of the bowstring in order to increase the potential energy stored in the bow limbs and thereby increase the power, speed, trajectory and penetration of the arrow. A particular advantage of the adjuster of this invention is that it allows the bow draw weight to be increased while the bowstring is pulled back. There are several desirable results from that capability which are subsequently described.
Archery is a historically traditional as well as a modern sport that is enjoyed for both competition and for hunting. Over the last half century, the compound bow has become a popular option for archers because of its advantageous characteristics. As with all bows, the limbs of the bow are cantilever springs that are fixed at their inner ends to a central frame called a riser and attached at their outer ends to a bowstring. The limbs store potential energy as they are bent back, within their elastic limit, by the force of an archer's arm drawing back on the bowstring. The most important characteristic of the compound bow is that the energy stored in its limbs, at a selected or standard draw length, is greater than the energy stored in a conventional bow and the draw force required to hold the bowstring at full draw is not only less than the maximum draw force (draw weight) required to draw the bowstring to full draw but also is considerably less than the draw weight of a conventional bow (which is maximum at full draw).
As the bowstring of a compound bow is drawn back, the draw force initially increases but, as the bowstring approaches full draw, the draw force is reduced. As a result, the archer is able to retain the bowstring at full draw while exerting a considerably smaller force on the bowstring than the maximum draw force of the compound bow and at an even smaller draw force than a conventional bow. The “let off” is the draw force reduction for a compound bow and can be as much as 70% to 80%. Additionally, at full draw the energy stored in the limbs is considerably greater than the energy stored in a conventional bow even though the draw force at full draw is considerably less. The ultimate result is that the archer is able to hold the bowstring at full draw with less draw force while simultaneously having more potential energy stored in the limbs for powering the arrow along its trajectory.
Another valuable characteristic of more sophisticated compound bows is that the tension force applied by the limbs to the bowstring, and therefore the potential energy stored in the limbs, is adjustable. This is possible because the butt end of each limb is pivotable within a limb pocket. There is a limb pocket mounted at each end of the bow's riser, one pocket for each limb. A loading end segment of each limb, which is the segment between a limb pivot and the butt end of the limb, has a limb bolt extending through a hole in the loading end segment and into anchoring attachment in the riser. Rotation of the limb bolt, or a nut on the limb bolt, in one direction forces the loading end segment of the limb closer to the floor of the limb pocket to increase the bend of the limb and thereby increase the potential energy stored in the limb. Alternatively, rotation of the limb bolt or its nut in the opposite direction allows the loading end segment of the limb to move away from the floor of the limb pocket to decrease the stored energy. However, these adjustments in the prior art bows can be made only when the bow is not in use for shooting an arrow.
Unfortunately, as the limb tension force is adjusted in a prior art compound bow, the required draw force is also changed. Increasing the potential energy stored in the limbs in the above-described manner increases the required draw force at all draw positions of the bowstring. However, a natural characteristic of humanity is that some archers have greater hand, arm and shoulder strength than others. Consequently, when the limbs are adjusted to increase the stored potential energy, the archer is required to apply a greater force to the bowstring. As the bowstring is drawn back, the initial draw force required by a compound bow is greater than the initial draw force required by a conventional bow. As the bowstring continues being drawn back, the required draw force increases even further beyond the draw force required by a conventional bow until the draw force reaches a maximum draw force. Only after reaching the maximum draw force does continued draw back result in the required draw force falling considerably below the maximum and considerably below the draw force for a conventional bow.
This operational characteristic means that, if a prior art bow is adjusted to increase the potential energy stored in its limbs, an archer with less strength must apply an increased initial and maximum draw force in order to reach full draw. Although the characteristics of the compound bow and the possibility of increasing the stored potential energy are of value to most archers, the requirement for increased initial and maximum draw force may require a draw force that is beyond the archer's practical strength. Consequently, such an archer may not be able to increase the stored potential energy with a prior art bow.
It is therefore an object and purpose of the present invention to provide a draw weight adjuster that permits an archer to increase the potential energy stored in the limbs without any increase in the required initial or maximum draw force.